Initial alkalinity requirement and effect of alkalinity sources in sulfur-based autotrophic denitrification barrier system

Abstract

The present study describes the effects of initial alkalinity and various solid alkalinity sources such as calcite, dolomite, and oyster shell on nitrate removal in a sulfur-oxidizing autotrophic denitrification process. The results showed that denitrification rate increased as the initial alkalinity present in the system increased. Denitrification rates determined by a half-order kinetic model were 0.269, 0.976, 2.631, and 3.110 mg NO3-N-1/2/L-1/2 center dot day corresponding to the initial alkalinity of 300, 600, 1,200, and 1,800 mg CaCO3/L, respectively. This amount of consumed alkalinity closely matched the theoretical alkalinity requirement. However, when 300 mg CaCO3/L of alkalinity was initially present the sulfur-based denitrification was greatly inhibited. The data indicate that approximately two times initial alkalinity of theoretically required alkalinity is needed for a desirable sulfur-based denitrification reaction. The initial alkalinity dissolution rates were 88, 38, and 14 mg CaCO3/L center dot day from 5 g of oyster shell, calcite, and dolomite, respectively. Accordingly, only 1.6 and 5% of initial nitrate remained in 7 days for oyster shell and calcite, respectively, but about 15% was still detected when dolomite was used.